Efficient irrigation of large fields with sprinklers requires that a relatively small number of sprinkling nozzles be moved over the field. One method of accomplishing this is to mount these nozzles on an overhead moving pipeline. The most prominent system now in use is called a center pivot and consists of an overhead pipeline supported by towers on wheels. The overhead pipeline rotates about a fixed point called the pivot. Water is supplied to the pipeline at this fixed pivot point and flows radially outward to the nozzles mounted on the pipeline. The resulting paths taken by the nozzles are concentric circles. Disadvantages of the center pivot system are adapting the circular pattern to square or rectangular fields and the fact that each nozzle travels at a rate proportional to its distance from the pivot point and must therefore be individually calibrated such that the rate of water application is as uniform as possible over the entire field.
Linear systems, sometimes called lateral move systems, also consist of an overhead pipeline supported by towers on wheels. Linear systems move perpendicular to the axis of the pipeline such that all points on the pipeline move at the same rate. Linear systems alleviate the two listed disadvantages of the center pivot system because their spraying patterns are rectangular and each nozzle sprays at the same rate, but they create another problem of their own. This problem is getting the supply water into the moving linear irrigation system. Because of this problem and the high cost of overcoming it with existing technology, linear systems are not now as widely used as are center pivot systems.
In general, there are two methods that are now in use to get supply water into a moving linear irrigation system. They are the ditch feed method and the hose drag method. The ditch feed method requires that there be an open ditch adjacent to or through the field carrying more water than is needed to irrigate the field. For the great majority of fields, this is not feasible, so that the hose drag method is now the most prevalent method of getting supply water into a moving linear irrigation system. A hose drag system consists of a hose attached at one end to a fixed hydrant and at the other end to the moving overhead pipeline system. The hose is doubled back on itself with a 180° bend so that it can accommodate the changing distance between the fixed hydrant and the moving overhead pipeline.
Hose drag systems are cumbersome and expensive. The length of hose that can be dragged is limited by the traction of the drive wheels of the linear irrigation system and this limit is generally less than desired. Thus, more than one hydrant is needed, which requires additional underground pipelines to the additional hydrants. Switching from one hydrant to the next is a significant chore that requires a shut-down of the system while the hose is dragged to the next hydrant. To accommodate the high flow rates necessary to irrigate large fields, the hose must be relatively large in diameter and therefore heavy when filled with water. Forces required to drag it are substantial. The hose itself must be strong enough to transmit these forces. The hose must also be flexible and resistant to wear. A smooth strip of land at least twice as wide as the minimum bending radius of the hose must be provided for dragging the hose, and this strip of land cannot otherwise be utilized. Clearly, there is a need for a better system for getting supply water to a moving linear irrigation system.
In 1971 U.S. Pat. No. 3,592,220 (Reinke) was issued for a LINEAR IRRIGATION SYSTEM WITH PICKUP SHOE. The patent discloses a system for withdrawing fluid from a stationary closed conduit at a continuously changing location in order to supply a linear irrigation system. However, a system using the concept disclosed in the patent is not available on the market.
In the aforementioned Reinke patent, it appears that the water conduit 104 must be rigid, and the water in the conduit must be pressurized in order to keep the slit closed in the top of the conduit. It further appears that the water pressure in conduit 104 is substantially the same along the full length of that conduit, both upstream and downstream from the pickup shoe 94. Another disadvantage of the Reinke system is that a peripheral seal 102 is required which is external to the conduit and extends the length of the pickup shoe. The seal is subject to leakage whenever the pickup shoe and the conduit are not in perfect alignment.
In 1980 U.S. Pat. No. 4,219,043 (Zimmerer et al.) was issued for Continuous-Feed Fluid Supply Apparatus. The patent describes apparatus for supplying water or other fluids from a stationary pipe to a moving pipe. A system using this concept is not available on the market. The stationary supply conduit has a seam which can be opened and closed somewhat like a zipper. An extractor is located inside the supply conduit and has a riser portion which protrudes through an opening in the seam. The extractor includes a generally cylindrical body portion. There is no description of a pump in the tube for pressurizing the water and pushing it upwardly. Apparently in Zimmerer's system the water pressure in the supply conduit is responsible for pushing the water out through the riser portion. This would normally preclude the use of thin-walled plastic conduits.
Other patents that disclose traveling openings in closed conduits are U.S. Pat. Nos. 3,903,917 (Ede); 3,011,502 (Jordan); 3,019,813 (Dormann); 2,974,876 (Poynor); and 4,576,335 (McAberg). None of these systems appear to have been commercialized, possibly due to leakage past the seals.
Another type of prior art includes the technology previously used in designs for closing plastic bags and is marketed under trade names such as ZIPLOC, HEFTY ONE, ZIP, GLAD LOCK, and others, and it is disclosed in numerous patents including U.S. Pat. Nos. 4,212,337; 3,173,184; 5,664,299; and many others.
There has not heretofore been provided a moving linear irrigation system which is able to effectively and efficiently remove water from a low pressure supply conduit and use that water in a moving sprinkler apparatus.